The present invention relates to a copper-clad board suitable for making a hole with a carbon dioxide gas laser, which copper-clad board is obtained by disposing a double-side-treated copper foil provided with a metallic-treatment layer having a high absorption rate of a carbon dioxide gas laser energy on at least one surface thereof, on at least an outer layer of a thermosetting resin composition layer such that the metallic-treatment layer is formed on a shiny surface of the copper foil which shiny surface is to be used as a surface layer, and laminate-forming the double-side-treated copper foil and the thermosetting resin composition layer under heat and pressure, a method of making a hole in said copper-clad board with a carbon dioxide gas laser, and a printed wiring board prepared from said copper-clad board. More specifically, the above metallic-treatment layer is a layer which can form an alloy with copper by the heating and the pressurization at the time of preparing the copper-clad board. The above copper alloy layer has properties that a penetration hole and/or a blind via hole having a small diameter can be made for absorbing a carbon dioxide gas laser when a copper foil surface is directly irradiated with a carbon dioxide gas laser. A high-density printed wiring board prepared by providing the above copper-clad board and making a hole having a small diameter in the copper-clad board with a carbon dioxide gas laser is suitably used for a small-sized and light weight semiconductor plastic package, a motherboard and the like.
Conventionally, a copper-clad board having a surface copper foil provided with a metallic surface-treatment which is capable of making a penetration hole and/or a blind via hole having a fine form by direct irradiation with a carbon dioxide gas laser, is not used for a high-density printed wiring board used for a semiconductor plastic package or the like. Further, attempts to make a hole by directly irradiating a copper foil surface with a carbon dioxide gas laser have been made. However, no hole is made with an energy of about 40 mJ since its bean is reflected. In this regard, there have been made attempts to use a double-side roughened copper foil having surface roughness of 3 to 5 mm. However, it is difficult to form a fine pattern, and no high-density printed wiring board can be produced.
Conventionally, drilling with a mechanical drill makes the penetration hole. In recent years, the diameter of the penetration hole becomes increasingly small, and designing is made such that the diameter of a hole is 0.15 mm or less. However, when a hole having such a small diameter is made, the problem is that the drill bents or breaks during the formation of a hole or that the processing speed is low, due to the small diameter of the drill, which results in problems in productivity and workability.
The blind via hole is made by etching and removing a copper foil in a position where a hole is to be made and then irradiating the position with a low-energy carbon dioxide gas laser. The above process includes steps of laminate-bonding of an etching film, exposure, development, etching, and peeling of the film. Therefore, much time is required so that a problem occurs in workability. Further, there is also proposed a method wherein a copper foil surface is oxidized to form a black copper oxide layer and the resultant surface is irradiated with a carbon dioxide gas laser, to make a blind via hole. In this case, the black copper oxide layer of the copper foil surface is easily peeled off by friction or the like and the problem is that no hole is made when the portion where the black copper oxide layer is peeled off is irradiated with the laser. Consequently, the above method is apt to bring about defective items.
There is also proposed a method in which holes having the same size are made in copper foils on front and reverse surfaces through negative films according to a predetermined method, further, a copper foil having similar holes made by etching is disposed as an internal layer copper foil and a hole reaching the front and reverse surfaces is made with a carbon dioxide gas laser. In this case, the problems are that the deviation of the position of the internal copper foil occurs and that spaces occur between lands on the upper and lower surfaces and the hole so that a failure in connection occurs and it is impossible to form lands on the front and reverse surfaces.
Further, in a printed wiring board which is increasingly highly-densified in recent years, the problems are heat-resistance, anti-migration properties, electric insulation after moisture absorption and the like.
It is an object of the present invention to provide a copper-clad board suitable for making a hole with a carbon dioxide gas laser, in which a penetration hole and/or a blind via hole can be made by directly irradiating a surface copper foil of the copper-clad board with a carbon dioxide gas laser, a method of making a hole in the above copper-clad board and a high-density printed wiring board containing the above copper-clad board.
It is another abject of the present invention to provide a copper-clad board excellent in workability for making a hole and free from the occurrence of defective items with regard to a hole owing to the formation of a metallic-treatment layer which has a high absorption rate of a carbon dioxide gas laser energy and which causes no peelings by friction on a surface copper foil of the copper-clad board, a method of making a hole in the above copper-clad board and a high-density printed wiring board containing the above copper-clad board.
It is further another object of the present invention to provide a high-density printed wiring board free from the occurrence of a short circuit and a breakage in a fine pattern by providing a copper-clad board which is free from a flaw, a dent and an attached resin on its surface copper foil.
It is still further another object of the present invention to provide a high-density printed wiring board excellent in heat-resistance, anti-migration properties and electric insulation after moisture absorption, a copper-clad board which is capable of providing the above high-density printed wiring board, and a method of making a hole in the above copper-clad board.
It is yet another object of the present invention to provide a method of making a hole, which method is suitable for making a hole having a small diameter in a copper-clad board and is used for preparing a printed wiring board excellent in the reliability of the hole having a small diameter with regard to connection.
According to the present invention, there is provided a copper-clad board suitable for making a hole with a carbon dioxide gas laser, which copper-clad board is obtained by disposing a double-side-treated copper foil provided with a metallic-treatment layer having a high absorption rate of a carbon dioxide gas laser energy on at least one surface, on at least an outer layer of a thermosetting resin composition layer such that the metallic-treatment layer is formed on a shiny surface of the copper foil which shiny surface is to be used as a surface layer, and laminate-forming the double-side-treated copper foil and the thermosetting resin composition layer under heat and pressure, to make an alloy of the metallic-treatment layer and the copper by the above heating.
According to the present invention, there is provided a copper-clad board suitable for making a hole with a carbon dioxide gas laser according to the above, wherein the metallic-treatment layer is a layer which contains nickel or nickel and cobalt as essential components.
According to the present invention, there is provided a copper-clad board suitable for making a hole with a carbon dioxide gas laser according to the above, wherein the thermosetting resin composition is a resin composition containing a polyfunctional cyanate ester monomer and/or a prepolymer of said cyanate ester as essential components.
According to the present invention, there is provided a copper-clad board suitable for making a hole with a carbon dioxide gas laser according to the above, wherein the double-side-treated copper foil is a product formed by attaching a B-staged resin layer to a surface opposite to the surface having the metallic-treatment layer.
According to the present invention, there is provided a copper-clad board suitable for making a hole with a carbon dioxide gas laser according to the above, wherein the double-side-treated copper foil is a product formed by attaching a resin sheet to a surface opposite to the surface having the metallic-treatment layer.
According to the present invention, there is provided a copper-clad board suitable for making a hole with a carbon dioxide gas laser according to the above, which copper-clad board is a copper-clad board obtained by disposing a protective sheet to one surface of the double-side-treated copper foil, at least partially bonding the protective sheet to the double-side-treated copper-foil and disposing a B-staged-resin-layer-attached resin sheet on the other surface of the double-side-treated copper foil.
According to the present invention, there is provided a copper-clad board suitable for making a hole with a carbon dioxide gas laser according to the above, which copper-clad board is a copper-clad board obtained by the use of metal-foil-carrier-attached copper foil(s) in which metal foil(s) is/are disposed to one surface or both the surfaces of the double-side-treated copper foil and the metal foil(s) is/are at least partially bonded to the double-side-treated copper foil.
According to the present invention, there is provided a method of making a hole in a copper-clad board, in which the metallic-treatment layer surface of the above copper-clad board is directly irradiated with an energy sufficient for processing a copper foil by means of the pulse oscillation of a carbon dioxide gas laser, to make a penetration hole and/or a blind via hole.
According to the present invention, there is also provided a printed wiring board obtained by making a penetration hole and/or a blind via hole in the above copper-clad board.